In Allahabad, northern India, a megacity of millions is sprouting up at the confluence of the Yamuna and Ganges rivers. For millennia, Hindu devotees have flocked to these holy banks to participate in a ritual cleansing known as the Kumbh Mela; this year’s Maha Kumbh Mela is a particularly auspicious iteration in cycles of these pilgrimages, which occur four times every 12 years. In 2001, nearly 70 million flocked to the Ganges’ shores here.